Lamp, filament, and process of making the same



Nov. 27, 1934. s. RUBEN 1,981,878

LAMP, FILAMENT, AND'PROCESS OF MAKING THE SAME Original Filed Sept. 25, 1929 INVENTOR 5,4 NUEL AuBHv HY Wm Patented Nov. 27, 1934 UNITED STATES PATENT OFFICE LAMP, FILAMENT, AND 'raocns's or MAKING THE SAME Samuel Ruben, New Rochelle, N. Y., assignmto Sirian Lamp Company, Newark, N. 1., a corporation of Delaware 3 Claims. (01. 176-132) This invention relates to incandescent lamps,

filaments therefor, and a process for making the same. More specifically, the invention pertains to an incandescent lamp of the filamentary type 5 in which an improved coated filament is employed.

Among the objects of the invention is to provide an electric lamp construction of the filamentary type in which greater efficiency in operation is available than may be obtained from the ordinary tungsten lamp.

Another object is to provide a filament for an electric lamp which has a coating of material selective for luminous radiation and which at the same time does not absorb an unusual amount of energy through heat losses.

An object also is to provide a lamp of the type specified in which the filament is coated with a material having a low vapor pressure in conjunc- 20 tion with relatively high resistance to the passage of electricity at normal operating temperatures.

Still another object is to provide a coated filament for use in electric lamps which resists deterioration due to chipping and fracture arising from heat variation in the use of the filament as an illuminant.

Various other objects will be apparent from the description following and from consideration of the accompanying drawing, in which Fig. l is an elevation of an electric incandescent lamp embodying my invention;

Fig. 2 is an enlarged view of a short length of filament as used in the lamp of Fig. 1 and illustrating an improved coating; and

Fig. 3 is a sectional view of the filamentary construction of Fig. 2.

In an ideal lamp at least three characteristics should be present. The filament of a lamp should be of highlyrefractory material so that the lamp can be operated at high temperatures, inasmuch as the illumination energy varies as the fourth power of the temperature. The lamp filament also should be of such a material as to radiate selectively the luminous radiation in order to further amplify the efficiency. Radiation of this type is present in the ceria-thoria mantle of the Welsbach burner and also in the Nernst lamp. An ideal lamp should also be of material -of relatively low vapor pressure, so that the lamp will successfully stand a life test without bringing about discolorations inside of the envelope due to evaporation of the filament material.

Referring to the drawing, numeral designates the transparent envelope of the lamp, which envelope is attached to the usual base 11.

on the molybdenum base.

0n the stem 12 within the lamp and mounted on the base 11 is the filament support rod 14 having the cross supporting arms 15 to which is attached the filament 13, the ends of which terminate in contact with'the lead-in wire within the stem 12;

As shown more clearly in Figs. 2 and 3, the lamp filament consists of a core or base 16 on which a coating 17 of highly refractory material is applied. In the present invention, I utilize for the core material a refractory metal such as tungsten, tantalum, molybdenum, or other similar metals. I have found molybdenum a satisfactory metal in this connection, inasmuch as it is ductile and has a relatively high melting point.

For the coating material, I employ the oxide of beryllium (B6203). My investigations have proven that oxides of metals of low atomic number are relatively more desirable for coating filaments for electric lamps, inasmuch as these oxides are highly refractory, as well as offering higher resistance to the passage of electricity when heated to normal electric lamp temperatures. The oxides of magnesium, aluminum, and beryllium have been found particularly desirable as possessing the properties above noted, andof these three oxides, beryllium oxide combines the advantageous factors most effectively. This oxide is not only practically a non-conductor when heated, thus eliminating current and electrolytic losses, but also has a low vapor pressure, tending toward a long lamp life, and is, moreover, susceptible to easy application of the filament. The oxide of beryllium, in addition, when heated to luminous temperatures, gives evidence of possessing selective characteristics for light radiation analogous to the selective characteristics of the thoria-ceria mixture of the Welsbach mantle.

The process of coating the molybdenum wire with the oxide of beryllium is as follows. Beryllium metal is powdered to a relatively fine state and incorporated with a solution of amyl acetate in nitrocellulose, such as that provided, for example, by dissolving sixteen ounces of nitrocellulose in one gallon of amyl acetate. This coat ing material is applied to molybdenum wire of the desired size which has been previously cleaned and the coating slowly heated so as to become thoroughly dried and firmly positioned Alternatively, the beryllium metal may be applied to the molybdenum base by means of a spray of the molten metal in a reducing atmosphere, such as hydrogen. The coating is made thick and the wire is then drawn to the desired size, this operation embedding the beryllium in the molybdenum. The wire-coated with beryllium metal is then heated, as by the passage of an electric current therethrough, to a point above the melting temperature of beryllium, that is, to about 1300 C. in an atmosphere of hydrogen. At this temperature the molten beryllium combining with the electric lamp, or it may be utilized. for other uses of resistance wire.

When heated in an oxidizing atmosphere, there is produced on the surface of the wire a layer of beryllium oxide, and in this form the filament is immediately available for use as a light giving material in lamps, or for other purposes. Where utilized in electric lamps of the type illustrated in Fig. 1, the wire filament, prior to oxidation, and consisting of molybdenum, for example, and coated with beryllium metal, is attached to the filament support and placed in the envelope 10. Before evacuation of the lamps and while possessing an air atmosphere, the lamps are heated to an oxidizing temperature so as to form the external coating of beryllium oxide on the filament.

Subsequently, the lamps are evacuated, and if desired, in order to 'further'increase the eficiency of the lamps, a small amount of inert gas such as argon, may be introduced into the envelope, the pressureof which need not ordinarily exceed seventy millimeters of mercury..

In accordance with the above disclosure, I have developed a filamentary material having high utility for incandescent electric lamp illumination, in that it possesses in large proportion the temperatures.

refractory substances such as tungsten or tantalum may be satisfactorily used. Although beryllium oxide is preferable, because of its low vapor pressure and high melting point, other oxides such as that of aluminum or magnesium may be used with satisfactory results. Where magnesium metal is employed, however, helium would have to be substituted for the hydrogen in the initial heating process, due to the fact that in the case of hydrogen, there is a chemical reaction between magnesium and hydrogen at high Other modifications than those mentioned may of course, be made in the details of the process and in the product, and, therefore, the terms of the claims should be broadly interpreted.

Having thus described my invention, what I claim is:

v 1. A filament for electric lamps consisting of molybdenum metal having a coating of beryllium and molybdenum mixture and an oxide of beryllium.

2. A filament for electric incandescent lamps comprising a molybdenum core, an intermediate layer of molybdenum and beryllium metal mix-' ture, and an outer coating of beryllium oxide.

3. A process of making a filament for an electric'lamp which consists in spraying molten beryllium metal in a reducing atmosphere on a filamentary core of molybdenum, heating the wire thus coated, in a reducing atmosphere to a temperature above the melting point of the beryllium to bring about an alloy of beryllium and molybdenum on the surface of the wire, and subsequently heating the wire to bring about oxidation of the beryllium in the alloyed wire surface. 115

/ SAMUEL RUBEN.

requisite characteristics of selectivity, low va- 

